1. Field of the Invention
The present invention relates to an optical component mainly suitable for such a devices as gain equalizers for equalizing the gain of amplification of signal light in optical amplifiers, an optical amplification module incorporating the optical component, and an optical transmission system incorporating the optical component.
2. Related Background Art
The optical amplifiers are provided with an optical waveguide doped with a fluorescent substance which can be pumped by pumping light, and a pumping means for supplying the pumping light into the optical waveguide, and are provided in repeaters or the like in optical transmission systems. Particularly, in the case of the optical amplifiers applied to the WDM (Wavelength Division Multiplexing) optical transmission systems for transmitting signal light in which a plurality of signal channels of mutually different wavelengths are multiplexed (multiplexed signal light), it is important to amplify the plurality of signal channels included in the signal light all together at an equal gain and to keep optical powers of the plurality of signal channels stably at a target value. In order to equalize the gains of amplification of the signal channels in the optical amplifier of this type, therefore, an optical component like an optical filter having a loss spectrum of shape similar to a gain spectrum in the optical waveguide is used as a gain equalizer.
For example, Document 1 (K. Inoue, et al., “Tunable Gain Equalization Using a Mach-Zehnder Optical Filter in Multistage Fiber Amplifiers,” IEEE Photonics Technology Letters, Vol. 3, No. 8, pp. 718–720 (1991)) describes the technology of achieving gain flattening of the optical amplifier with an optical filter having a Mach-Zehnder interferometer. Document 2 (H. Toba, et al., “Demonstration of Optical FDM Based Self-Healing Ring Network Employing Arrayed-Waveguide-Grating ADM Filters and EDFAs,” Proceedings of ECOC '94, pp. 263–266 (1994)) describes the optical filters in the configuration in which two optical filters as described in Document 1 above are cascaded.